Recent years have witnessed optical disks such as CD-RW (Compact Disk Rewritable) and DVD+RW (Digital Versatile Disk Rewritable) being used extensively as rewritable recording media. With large numbers of these rewritable recording media in circulation, the need exists for better compatibility between recording apparatuses for writing data to these disks on the one hand, and reproducing apparatuses, especially those with no means to record data to such disks on the other hand. For the sake of convenience, it is preferred that data be reproduced from rewritable optical disks also by the reproducing apparatus incapable of wring data to such disks.
Optical disks such as CD-RW and DVD+RW to and from which data can be written and read randomly come in one of two states: either they have no data recorded in their recording regions, or they have both data-filled and data-free regions located side by side on a single disk.
When there is no data recorded in the recording regions of an optical disk, the recording and reproducing apparatus with means to write data can extract synchronization information for determining the physical addresses of the recording regions out of an acquired wobble signal. The wobble signal is obtained (i.e., detected) by emitting a light beam (laser) to a slightly meandering track of the recording regions.
Where there is data recorded in the recording regions of an optical disk, the recording and reproducing apparatus acquires a reproduced signal from the disk by emitting the light beam to the pits formed in these regions. From the reproduced signal thus obtained, the recording and reproducing apparatus can extract (i.e., acquire) synchronization information for determining the physical addresses of the recording regions together with the data which was retrieved from the recording regions and which contains the synchronization information.
The reproducing apparatus with no means to write data, by contrast, works on the assumption that data is reproduced from a data-filled optical disk, i.e., from an optical disk with no data-free recording regions. The reproducing apparatus can extract from the reproduced signal the synchronization information for determining the physical addresses of the recording regions. Unlike the recording and reproducing apparatus, however, the reproducing apparatus has no facility for extracting the synchronization information from the above-mentioned wobble signal.
That is, the reproducing apparatus is incapable of reproducing data from optical disks with no data-filled recording regions or from optical disks each containing both data-filled and data-free regions. The reason is that from any data-free recording region on the optical disk, the reproducing apparatus cannot extract (obtain) data synchronization information.
The recording and reproducing apparatus thus needs to format the entire optical disk so that the reproducing apparatus may randomly reproduce the data recorded randomly on the optical disk. The formatting involves writing dummy data to the whole recording regions of each optical disk.
Illustratively, if a data-free optical disk (i.e., blank or virgin disk) is mounted on the recording and reproducing apparatus, the apparatus formats the disk by writing dummy data to the whole recording regions of the mounted disk. It takes a lot of time for the recording and reproducing apparatus to format all recording regions of the mounted optical disk. An extended period of time typically elapses before the formatting is completed and the optical disk is ready to be used by the user. In other words, following the mounting of an optical disk (blank disk) on the recording and reproducing apparatus, the user must wait a long time for the disk to be completely formatted for use.
It is obvious that after mounting an optical disk on the recording and reproducing apparatus, the user expects to have the disk readied for use in the shortest possible time.
Some techniques have been proposed to bypass the above difficulty. The techniques involve first completing initialization of (i.e., writing of necessary data to) the lead-in area of a rewritable single-layer optical disk, the area accommodating information about the data to be recorded to the recording regions of the optical disk. With the lead-in area initialized, a host device such as a personal computer connected to the recording and reproducing apparatus is allowed to access the mounted optical disk. Thereafter, while the recording and reproducing apparatus is at rest (in idle state), dummy data is written to data-free regions (i.e., unrecorded regions) in the user area to which to write the data designated by the connected host device (i.e., user) in what is known as a background formatting process (See Patent Document 1).